Chemistry World Podcast -September 2010
00:12- Introduction
01:15- Recycling CO2 to make plastic
03:15- Snapshots of mystery molecules
06:10- Allison Carey from Yale University, US, on how mosquitoes sniff out meals and the chemicals we might use to stop getting bitten
13:29- A MOF you can scoff
15:54- Buckyballs give clue to space mystery
19:10- Graham Hutchings from the University of Cardiff, UK, talks about the mystery and allure of gold on the nanoscale
27:50- Bubble powered microengines push forward
30:28- Light-rechargeable batteries
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Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.
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Interviewer -Ben Valsler
This month: making plastic from thin air or at least from waste carbon dioxide; A MOF that you can scoff and that's an edible metal organic framework not an insect that likes light bulbs; and bubbled powered microengines, how catalysts can make these tiny jet engines faster and more efficient; plus the molecular receptors that help mosquitoes spot our distinctive aroma.
Interviewee - Allison Carey
The types of compounds that we tend to admit are things like aromatic compounds like indole, phenol, they smell kind of stinky. We work with them in the lab and they do smell a lot like dirty gym socks or something like that, they're not pleasant to work with.
Interviewer -Ben Valsler
And we explore the catalytic capacity of gold nanoparticles. I'm Ben Valsler, and for this the September edition of the Chemistry World podcast, I'm joined by Nina Notman, Matt Wilkinson and Mike Brown.
(Promo)
The Chemistry World Podcast is brought to you by the Royal Society of Chemistry. Look us up online at chemistryworld dot org.
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Interviewer -Ben Valsler
To get us started this week, a new way to make plastic from pollution. Tell us more Matt.
Interviewee - Matt Wilkinson
Yes Ben. The US company called Novomer has been awarded a 18.4 million dollar grant to turn thin air or actually carbon dioxide into plastics and the type of plastic that they're going to be turning them into is a type of polycarbonate polymer and these are used to make all sorts of things from plastic bottles, laminates that coats CDs, you name it, there is polycarbonate in them.
Interviewer -Ben Valsler
So, how are they actually doing it?
Interviewee - Matt Wilkinson
Right, so what they do is they take a carbon dioxide stream from a waste source from an industrial process. Then they use a cobalt catalyst that Novomer's Chief Executive, Jim Mahoney describes it as a relatively complicated but easy to handle cobalt catalyst and these then react with CO2 and an epoxide molecule and they form various weights of polymer and they can control the weight of the polymer formed by throwing in what they call a branching agent. So they can basically control of the weights of the plastics and therefore they can make them applicable to a whole range of applications and incredible control over that molecular weight.
Interviewer -Ben Valsler
So, this makes them an ideal, sort of, normal feed stock that can go into normal plastic production.
Interviewee - Matt Wilkinson
Absolutely, the plastics they actually make already are known from the petrochemical sources and they can create them with a maybe a little bit more controlled in some ways, and of course rather than using oil which is becomingly increasingly expensive to use, they're using a waste product which many countries are investing lots of money into figuring out ways to bury underground. This might make a lot more sense to actually rather than bury it and turn it into something useful.
Interviewer -Ben Valsler
So, it won't help to reduce their reliance on plastics, but it should help to reduce the reliance on the oil that we use to make them in the first place.
Interviewee - Matt Wilkinson
Definitely, yes, and it should also have some plastic production from, you know, environmentally friendly and sustainable.
Interviewer -Ben Valsler
Thanks Matt. Mike we've been looking at a new way of identifying the structures of chemicals as well this week.
Interviewee - Mike Brown
Yeah, that's right. So a team of scientists at IBM in Switzerland in collaboration with colleagues at the University of Aberdeen in Scotland have used a form of microscopy to image molecules to determine their structure. So, in Chemistry, especially with natural product synthesis, identifying structures is quite a problem and traditional techniques such as Nuclear Magnetic Resonance--which is NMR--sometimes has difficulty identifying structures. You can go so far with the techniques we've got, but you sometimes come out with possible structures and you may have four possible structures. So, it's a challenge to find out what the structure actually is, and the team, IBM have used atomic force microscopy which is where there's an atomically sharp tip mounted on an oscillating spring. This moves near a molecule, which is mounted on a surface and when the tip becomes near the molecule, it changes the vibrating frequency that it's oscillating at and this is called a detuning and all these detuning is depending on what atom you're over, will cause a different vibration and then these can be recorded and converted into dark and light areas and build up an image. So, what the guys have been doing is building up this image and from the image they can see that two of these possible structures from the NMR spectrum are total rubbish and then they've got two other structures, which they can use calculations to prove which one is actually the correct structure.
Interviewer -Ben Valsler
So, what chemical have they actually been looking at?
Interviewee - Mike Brown
Okay, so they've been taking a natural product which the guys at the University of Aberdeen are interested in, which is called cephalandole A. The reason they've been looking at this is because in the past, the reported structure has been found to be wrong.
Interviewer -Ben Valsler
As it's something that we didn't know the structure of and we had these four options, how can we be certain that this technique actually works?
Interviewee - Mike Brown
About a year ago, the guys at IBM used a technique to prove that it worked. They used pentacene which is a known structure, it's a planar structure and they successfully imaged pentacene. So, we know from other analytical techniques that this structure determination using this method is correct, but now we're taking a step further. Instead of proving structures that are already known, we're finding out structures that are unknown. So, in reality you could in the future use this technique in the pharmaceutical industry, or you know, in the lab in conjunction with NMR to actually prove unknown structures and speed up the process.
Interviewer -Ben Valsler
So, vibrations on the molecular scale can help us to determine the exact structure of the whole host of unknown chemicals, thanks Mike.
Interviewer -Ben Valsler
The structure of a molecule often dictates how it responds to other molecules and so it can be very useful in understanding how biological systems will respond to a chemical stimulus. This is essential in understanding how biting insects such as mosquitoes will find their hosts and can lead to new and better ways to prevent bites and transmission of disease. I spoke to Dr Allison Carey at Yale University.
Interviewee - Allison Carey
So, we've been looking at how mosquitoes smell and in particular we've been looking at the Anopheles gambiae species, which is the major vector of malaria in sub-Saharan Africa and the species of mosquito Anopheles gambiae relies heavily on its sense of smell to find its human blood meal targets. So, we've been looking at the molecular basis for this process.
Interviewer -Ben Valsler
So, what is it in particular about the mosquitoes themselves that you're looking at? Are you dissecting mosquitoes to look at what's going on in their antennae?
Interviewee - Allison Carey
We're sort of doing that at a molecular level. We've looked at the odour receptors. And so, this is a big family of about 80 proteins, their membrane receptors that bind to volatile chemicals and these were identified first in the model organism Drosophila melanogaster about a decade ago now. And they were more recently identified in Anopheles gambiae, the genes where and we set about to functionally characterise these odourant receptor.
Interviewer -Ben Valsler
So we're looking to find out what chemicals these receptors actually respond to? How specific are they?
Interviewee - Allison Carey
So, it varies. That's an interesting question. So we, sort of, systematically looked at as many of the receptors as we could. As I have mentioned about 80 of them and we're able to look at about 50 of them. For various technical reasons, we couldn't study all of them and then we found that some of the receptors are not so specific, so buying to of the hundred of the compounds we tested, they might be activated by 20 or 30 of them pretty strongly and then we found some other receptors that are extremely specific and they out of, you know, 100 plus compounds that we tested may be activated by just two or three. And so we thought that was interesting actually that some of the receptors are sort of specialists and others are more generalists. I mean also did note that there's a continuum, it's not a decision of just specialists and generalists, but there's a sort of a continuum and what we call the tuning of the receptor.
Interviewer -Ben Valsler
Mosquito receptors are, they help guide the mosquito through its world, but it's not just looking for animals to bite, it's also looking for mates and for sugar meals when they need them. How can we tell which are the important receptors with regards biting us?
Interviewee - Allison Carey
At this stage in the research, we can't be certain which of the receptors that we've studied are for sure playing a role in guiding the mosquito to its human host, but there's a lot of literature out there about what sorts of chemicals humans release. So, what comes off our skin from sweat, from bacterial breakdown products of sweat and skin and there are many papers about that and sort of the types of compounds that we tend to emit are things like aromatic compounds like indole, phenol, they smell kind of stinky, we work with them in the lab and they do smell lot like dirty gym socks or something like that. They're not pleasant to work with. And things that come from plants, you know, there's also huge literature on this sorts of chemicals that plants and fruits would have made and those tend to be things like esters and aldehydes and ketones and again if you open up a bottle of an ester, it smells very fruity, it smells like a banana or like an apple. So, we do have information from other people's research about the types of chemicals generally that are emitted from people versus from plants and certainly there's a lot of overlap between the two of those. No known human specific odourant or no known plant specific odourant, but more sort of general trends of the types of the compounds that'd be coming from different sources.
Interviewer -Ben Valsler
So can we start to look at the receptors, look at the chemicals they're specific for and work on which ones we need to target to try and reduce things like malarial transmission?
Interviewee - Allison Carey
So that's the idea. So, we feel that we've come up with some good targets because we've identified some receptors, particularly specialist receptors that respond to compounds that have been identified as coming from human sweat or human emanation. And we think that these are really interesting potential targets and play a role in the behaviour of the mosquitoes, so the next step is to test this hypothesis behaviourally and to do that we're collaborating with a group that specialises in mosquito behaviour and they're right now testing some of the compounds that we've identified as activating these receptors and to see if they can get an attractive behaviour to these compounds and then the next step after that might be to look for compounds that could inhibit the receptor responses and therefore may inhibit the behavioural response.
Interviewer -Ben Valsler
So, what are the options for inhibiting this response? Do we need to block the receptor? Do we need to find another chemical that will deactivate the receptor?
Interviewee - Allison Carey
That's a great question. So there are, sort of a, number of ways we could go about it. One idea is to find another chemical that blocks the response to the first chemical and we've identified some candidates there and we can try to test those. Another idea is that could we find a compound that sort of, super-activates the receptor, so it just sort of, has a very sustained response perhaps and sort of jams the receptor. It's been shown in other insects that the temporal dynamics of an odourant receptors response are important for guiding the animal that it provides information about the odourant identity. And so if we can, may be disrupt the temporal dynamics of the response that might be useful as a way to inhibit or repel the mosquito. It's also possible, there's some evidence for repellent channels, so you might activate a neuron and that neuron, or the receptor and the neuron spread out a repellent pathway. So activating doesn't always correlate with attraction and if you put your hand on a stove, you know your receptors and neurons are activated certainly but it's a negative response to that activation, so similarly if we could identify some receptors that are part of a repellent pathway, could we find activators for those receptors. So I think there are a number of ways we could look for things that could be behaviourally active.
Interviewer -Ben Valsler
Yale University's Allison Carey on ways to interrupt the mosquito's sense of smell and so cut back on the burden of mosquito-borne diseases like malaria.
Interviewer -Ben Valsler
Now if all that talk of sweaty gym socks hasn't put you off your dinner, Nina has news of a new edible chemical structure.
Interviewee - Nina Notman
Indeed we have. So this work which has been done by Fraser Stoddart at North-western in the US, he's been looking at MOFs which are metal organic frameworks, made from molecules which have been approved for human consumption, so these frameworks which are networks of metal nodes connected by organic struts have been considered for various applications such as storing gas or delivering drugs. There's hope that being able to make edible version of these molecules might have applications in the food and pharma industry. So, Fraser's team is actually intending to look at new interlocked molecular architectures and falling upon these edible MOFs was actually a bit of an accident. In the lab, they were taking the eight-membered sugar ring gamma-cyclodextrin which is a local derivative of starch and dissolving it with potassium hydroxide, which is a salt substitute in water. They then diffused ethanol for the system and found they got well-defined colourless crystals. They then looked at the crystals using x-ray and found something quite unexpected, which was 6 cyclodextrin rings formed the faces of a cubic structure and these cyclodextrin rings were held together using coordinating potassium ions with an open pore in the centre. They saw that these cubic structures, many of them fitted together to form a large 3-D cubic framework, so it's a standard kind of framework of a MOF. They then looked at the possible uses of the MOF. So, one of the standard tests is to see how much nitrogen will stick into the pores and they found that these edible MOFs observe the same amount of nitrogen as many of the other MOFs which are out there. Apart from the fact that they're edible another big advantage of these MOFs is that most of the ones which are available at the moment come from petrochemical feed stocks where these are obviously a carbon neutral source.
Interviewer -Ben Valsler
So much like making plastic from CO2 we were talking about earlier, this would reduce our reliance on oil. I've heard of MOFs being put forward as things for carbon capture devices but what could the pharmaceutical industry get out of them?
Interviewee - Nina Notman
The pharmaceutical industry are very interested in controlled drug delivery and the pores in the centre of these frameworks could be used to store the drugs and then they would presumably the MOFs would dissolve as they got to vibrate in the body.
Interviewer -Ben Valsler
And the fact that they're edible compounds means that we are not eating something toxic. Thank you very much.
(15:54 - Buckyballs give clue to space mystery)
Interviewer -Ben Valsler
Getting from inner space to outer space we found mysterious Buckyballs floating around in between the stars, tell me more.
Interviewee - Matt Wilkinson
Yes, Ben, researchers led by Jan Cami of the University of Western Ontario in Canada have discovered huge clouds of these Buckyballs which are 60 or 70 carbon atoms in spherical football-shaped structures and there's a fascinating story about how they actually discovered them. Many years ago when Sir Harry Kroto and his team at the University of Sussex were looking for structures out in space they came across these what they believed to be carbonaceous compounds in between stars. But they never quite figured out exactly what they were. They then went in to the laboratory and actually made these C60 molecules and that ended up winning Sir Harry Kroto a Nobel Prize. But even once they had them and actually managed to fully characterise them, they've never been particularly identified out in space. People have guessed that the signals they've seen have possibly been due to these types of molecules but they've never been able to get really conclusive proof. So what has happened now is that using the on-board infrared spectrometer on the Spitzer space telescope, they focused in on a particular area of the universe and said the planetary nebula Tc 1 which is about 6000 light years away and they've managed to find the four vibrational peaks that you would expect to find from the C60 Buckminsterfullerene molecule. Why they haven't found those peaks in other places is probably due to the fact that these are from a nebula, in material that has been blown off a star, so it's all still very, very hot and so there's still emitting lots of radiation; whereas if you look in the background the general space that they are interested of space, you know, the gap between the stars that's all quite cold and so not emitting very much radiation which is why we can't see it even though its probably there. And what's amazing about these gas clouds is that they probably contain around 1023 kg of material which is about enough to make a planet one and a half times the size of the moon, so it's just a phenomenal mass material in these big gas clouds.
Interviewer -Ben Valsler
So, we've gotten from not being able to find it, the thinking is that finding quite an enormous amount of it just due to the fact that it was quite warm. You said that we suspected it was there before we saw hints, how can we be certain that this is definitely a signature of Buckyballs?
Interviewee - Matt Wilkinson
Well the fingerprint that you see in the infrared spectra is exactly the same as those that you would see if you heated up these molecules to the sorts of temperatures that they expect Tc 1 to be at, they're exactly replicated in the spectra that you would see on earth.
Interviewer -Ben Valsler
Thanks Matt, so at last we found Buckyballs in space and more than enough to make a full size model of our own moon.
Jingle
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Interviewer -Ben Valsler
You're listening to the Chemistry World podcast with me Ben Valsler. Still to come we've got more chemistry news and our side splitting chemistry joke of the month.
Interviewer -Ben Valsler
But now nanosize particles of gold are showing great promise in a number of applications from production of hydrogen peroxide to selective oxidation of hydrocarbons. But gold itself has long been understood to be a very unreactive metal. Graham Hutchings Professor of Physical Chemistry and Director of the Catalysis Institute at Cardiff University explained why for catalysts at least people are going for gold.
Interviewee - Graham Hutchings
I think we feel that gold is a catalyst is simply there's a perception that gold would not be an active material. It suddenly amazed people and a number of people started to think that gold is not only going to be the best catalyst for carbon monoxide oxidation and for certainly in hydrochlorination which were the first two reactions where it was shown to be by far the best catalyst but in fact it can do everything and so you'll find in the literature at the moment everybody trying gold for everything and but is it is a tale that it was something which is the most noble of metals is immutable and therefore why should it suddenly be one of the best catalysts and that has just caught everybody's imagination?
Interviewer -Ben Valsler
And what do you have to do to take this very unreactive metal and cause it to be a catalyst?
Interviewee - Graham Hutchings
That's the exciting bit. A lot of people will be familiar with the terms nanochemistry but we aren't into chemistry of nano because it deals with things that the nanoscale of molecules are effectively nanomaterials. And in this case if you take gold and divide that down to a few atoms then it takes on a very reactive character and so in CO oxidation people have considered that this very, very small nanoparticles of gold which is the active species, now whether they're gold metal all they can think cationic or anionic species with the trend has been in people's mind is that the smaller the particle the more active it is for a number of reactions. And this has been a trend in microscopy as well and that of people have even proved with microscopy now with something known as aberration corrected scanning transmission of electron microscopy, one can actually see single gold atoms against the right supporting matrix. We are now able to know that actually collections of seven to ten gold atoms are associated with very high activity for CO oxidation and so that really is the nanoscale. And people weren't able to pick this up before and so until the 1980s when it was shown by Masatake Haruta that small gold nanoparticles were very active to CO oxidation and it couldn't be pinned on impurities, it really was gold. And at the same time when I showed that cationic gold was the best catalyst for settling hydrochlorination then it became apparent that there really was something and it wasn't just in artefact or impurities still going on.
Interviewer -Ben Valsler
So, why do we think it is that gold on the nanoscale should have this effect but on the microscale it loses it completely?
Interviewee - Graham Hutchings
Well, this is probably to do with the electronic structure and it's still a matter of controversy as to why this happens. So, if you were to ask 10 scientists in the room on the action of gold I am sure you'll get 11 answers on this one. Basically, if you go down to below to nanometres for a particle of gold, so you've got a collection still of several hundreds of those atoms at that level, you lose the band structure of the metal, or the electrons that are not moving in the way that they were, so it loses its metallic structure and so at that point people associated large amounts of catalytic activity with it. I suspect that this is a mixture of electronic factors and also the interface with the support that one puts these nanoparticles on. So, the supporting matrix which could be an oxide or carbon makes a big impact on the catalysis that's observed and so one has the sides of the interface between these nanoparticles and the oxide or the carbon support and that changes the electronic nature because you've got the electrons coming from the support organ to the support as well. So long answer, it's a matter of immense controversy at the present time and I'm certainly not going to put my head above the path.
Interviewer -Ben Valsler
Does the actual structure of the nanoparticles affect its properties as well? Does it matter what shape it is?
Interviewee - Graham Hutchings
Yes, that's a very good question indeed. When you've got something which is seven to ten atoms, then the materials are likely to be bi-layers with perhaps five to six atoms on the bottom and one or two atoms on the top. The five or six atoms are associated with the support that's got a very strong interaction with that support. Then you've got the layer above the atom, so people consider that safer CO oxidation. The CO would be activated on the top layer and the oxygen would be activated at the side interfacing with the support matrix. As you go bigger in particles, obviously the morphology of that structure changes. But you still end up with these interfacial sides which are likely to be key in the catalysis that's observed.
Interviewer -Ben Valsler
Of course, one thing that, I guess, most people when they think of gold is cash, the value. Is this expensive work to do or does this actually work out cheaper than doing the same sorts of reactions with existing catalysts?
Interviewee - Graham Hutchings
Gold of course is considered to be an expensive metal, it's a bullion metal, it's traded only in the world markets and goes up and down with the winds of the markets and I suppose at this moment, it's very expensive indeed somewhere between a 1100 and 1200 dollars per ounce, but in terms of a catalyst, the metal component of the catalyst is not a matter of expense and of course platinum and other metals, which are also precious are used regularly as catalysts and platinum and palladium are very expensive metals and they're used in car exhaust catalyst and so the general public will all be driving around using precious metal catalyst. So, the amount of the dust at the side of the roads is not considered to contain a measurable amount of platinum metal and so it might be worth at some point trying to extract it from that source. Although gold could be considered to be expensive, I don't think its price is going to preclude it from being commercially exploited.
Interviewer -Ben Valsler
And just finally what do you think the next step will be? What's the next thing that we need to work out?
Interviewee - Graham Hutchings
Well, I think from a theoretical point of view, it would be really nice to nail why it is that gold is capable of doing certain reactions with such straight specificity, so our mechanistic understanding really helps to come up with speed. The second thought is really we need to get gold to break into a commercial application. The fact that gold is really active catalyst for carbon monoxide oxidation gives it possibility to be a commercial item in breathing apparatus. I know that there are current possibilities from a group in China and one thing which I haven't discussed earlier is that gold, when it's alloyed with other metals can improve this activity and so gold alloyed with palladium takes on much higher activity than gold alone for particular applications. So, there's a number of ways in which I would hope that gold will be commercialised. Then of course, once that happens, I think, things will open up and drive the field much better then.
Interviewer -Ben Valsler
Graham Hutchings explaining how even though we don't understand how it works, there are lots of opportunities for gold nanoparticles in Chemistry, perhaps heralding a nanogold rush.
Interviewer -Ben Valsler
And from nanocatalysts to micro jet engines lined with catalase, Mike.
Interviewee - Mike Brown
Yes Ben. So scientists in Dresden have developed microscopic jet engines powered by an enzyme that makes bubbles of oxygen from hydrogen peroxide as a fuel. So, these jet engines are made out of alternating thin layers of titanium and gold which are rolled up into tubes and on the inside of the tubes, they've attached catalase enzymes and catalase protects cells in the body from toxic effects of hydrogen peroxide by converting it into oxygen and water. So, the catalase inside the tubes makes bubbles of oxygen which propel the tube along and as the tube is moving forward, more hydrogen peroxide is being put into the top of the tube, which is then being converted into oxygen and so the process goes and goes and goes.
Interviewer -Ben Valsler
So, the exhaust gases, the oxygen are sort of acting like a chimney to put more fuel in the top end.
Interviewee - Mike Brown
Yeah, that's right. The interesting thing about these new microengines is that in the past, equivalent engines have been made, but using platinum catalysts instead. Now these new microengines are 10 times faster than these equivalent platinum catalyzed microengines. They can also get the same speed, but only use up one-tenth of the amount of the hydrogen peroxide fuel. So, they're more efficient. The problem at the moment is that we're still
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